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Needlecast Diseases

Needlecast diseases of evergreens are caused by several fungi. We have much to learn about when these fungi attack a tree, how long the fungus must be in the tree before needles are shed, when is the best time to apply a fungicide, and which chemicals provide the best protection.

However, progress is being made in these areas. Needles infected with fungi generally fall several months after the actual period of infection. The period of greatest infection for most needlecast fungi is during the late spring and early summer months. Symptoms, the visible indications that the needle is diseased, do not appear until the late winter, spring, and early summer of the next year.

All the needlecast fungi form small structures on the infected needle in which thousands of spores form. These "fruiting structures" may be black, orange-red, or tan, depending upon the fungus. Other fungi that grow on dead or dying needles but do not cause needlecast may form similar structures. Finding a fungal fruiting structure on a dead needle is not proof that the tree has a needlecast disease. Send a sample to the Plant Disease Clinic for verification.

Managing Needlecast Diseases

Needlecast fungi require abundant moisture for their growth and development. Therefore, plant so that the air circulation around trees will be good. Maintain good weed control so that tall weeds do not impede air circulation around the lower branches. Avoid planting susceptible trees in low or shady areas where humidity and needle wetness tends to be high for prolonged periods. Fungicides can be applied to protect healthy, new foliage. Even if a tree is sprayed, the needles that were infected during the previous year and that are showing symptoms this year will falling off the branch. But the new, protected needles will be free of symptoms next year and will remain on the tree. In the case of most needlecasts, the fungicide is applied as new needles are emerging. See other fact sheets on pine, Douglas-fir, and spruce diseases for details on controlling needlecasts on those trees.